1. Technical Field
The present invention relates to an improvement of a viewing angle characteristic of a liquid crystal display device.
2. Background Art
In liquid crystal display devices, optical films displaying various optical characteristics have hitherto been used for optical compensation corresponding to a mode thereof. For example, an optically compensatory film having an optically anisotropic layer composed of a liquid crystal composition on a transparent support composed of a polymer film is proposed as an optically compensatory film of a TN mode liquid crystal display device (see, for example, Japanese Patent No. 2587398).
Also, it is proposed to use a polymer film whose optical axis is inclined in the thickness direction for the optical compensation of a TN mode liquid crystal display device in place of the optically compensatory film having an optically anisotropic layer composed of a liquid crystal composition.
For example, JP-A-7-333437 and JP-A-6-222213 each describe a method of leading a film to pass through two rolls running at a different peripheral speed whereby a shearing stress is applied to the film to produce a film having a tilted optical axis, indicating the application of the film to TN-mode liquid crystal displays. However, the methods described in the documents have some problems in that the optical properties of the films produced greatly fluctuate and that the surfaces of the films are readily scratched.
JP-A2003-25414 and JP-A2007-38646 each propose a method of producing an optical film whose optical axis is inclined in the thickness direction by having a melt of thermoplastic polymer composition through the nip between two rolls running at a certain condition. According to the methods described in the documents, the above mentioned problem may be solved.
On the other hand, a liquid crystal display device is used as not only a display for personal computer, which is basically used by a single person but a display for television, which is observed by a plurality of persons from various directions.